Inks for ink jet printing comprising a tris-azo dye

ABSTRACT

Inks comprising a liquid medium and a tris-azo compound of Formula (1) or salt thereof: 
                         
wherein the liquid medium comprises water and an organic solvent.

This invention relates to inks of use in ink jet printing (“IJP”). IJPis a non-impact printing technique in which droplets of ink are ejectedthrough a fine nozzle onto a substrate without bringing the nozzle intocontact with the substrate.

There are many demanding performance requirements for inks used in IJP.For example they desirably provide sharp, non-feathered images havinggood water-fastness, light-fastness and optical density. The inks areoften required to dry quickly when applied to a substrate to preventsmudging, but they should not form a crust over the tip of ink jetnozzles because this will stop the printer from working. The inks shouldalso be stable to storage over time without decomposing or forming aprecipitate which could block the fine nozzles.

We have now devised an ink which is particularly useful for ink jetprinting.

According to the present invention there is provided an ink comprising aliquid medium and a tris-azo compound of Formula (1) or salt thereof:

wherein the liquid medium comprises water and an organic solvent.

When compound of Formula (1) is in the form of a salt preferred saltsare alkali metal salts, especially lithium, sodium and potassium salts,ammonium and substituted ammonium salts. Especially preferred salts aresalts with ammonia and volatile amines. The free acid form may beconverted into a salt using known techniques. For example, an alkalimetal salt may be converted into a salt with ammonia or an amine bydissolving an alkali metal salt of the composition in water, acidifyingwith a mineral acid and adjusting the pH of the solution to pH 9 to 9.5with ammonia or the amine and removing the alkali metal cations bydialysis.

The ink preferably comprises:

-   -   (a) from 0.01 to 30 parts of a compound of Formula (1) or salt        thereof; and    -   (b) from 70 to 99.99 parts of a liquid medium comprising water        and an organic solvent;        wherein all parts are by weight and the number of parts of        (a)+(b)=100.

The number of parts of component (a) is preferably from 0.1 to 20, morepreferably from 0.5 to 15, and especially from 1 to 5 parts. The numberof parts of component (b) is preferably from 99.9 to 80, more preferablyfrom 99.5 to 85, especially from 99 to 95 parts.

Preferably component (a) is completely dissolved in component (b).Preferably component (a) has a solubility in component (b) at 20° C. ofat least 10%. This allows the preparation of liquid dye concentrateswhich may be used to prepare inks and reduces the chance of the dyeprecipitating if evaporation of the liquid medium occurs during storage.

The weight ratio of water to organic solvent is preferably from 99:1 to1:99, more preferably from 99:1 to 50:50 and especially from 95:5 to80:20.

It is preferred that the organic solvent present in the mixture of waterand organic solvent is a water-miscible organic solvent or a mixture ofsuch solvents. Preferred water-miscible organic solvents includeC₁₋₆-alkanols, preferably methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol andcyclohexanol; linear amides, preferably dimethylformamide ordimethylacetamide; ketones and ketone-alcohols, preferably acetone,methyl ether ketone, cyclohexanone and diacetone alcohol; water-miscibleethers, preferably tetrahydrofuran and dioxane; diols, preferably diolshaving from 2 to 12 carbon atoms, for example pentane-1,5-diol, ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol, hexyleneglycol and thiodiglycol and oligo- and poly-alkyleneglycols, preferablydiethylene glycol, triethylene glycol, polyethylene glycol andpolypropylene glycol; triols, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether, cyclic amides,preferably 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone,caprolactam and 1,3-dimethylimidazolidone; cyclic esters, preferablycaprolactone; sulphoxides, preferably dimethyl sulphoxide andsulpholane. Preferably the liquid medium comprises water and 2 or more,especially from 2 to 8, water-soluble organic solvents.

Typically the liquid medium will further comprise one or moresurfactants, for example anionic and/or nonionic surfactants. Examplesof anionic surfactants include: Sulfonate surfactants such asSulfosuccinates (Aerosol™ OT, A196; AY and GP, available from CYTEC) andSulfonates (Aerosol™ DPOS-45, OS available from CYTEC; Witconate™ C-50Havailable from WITCO; Dowfax™ 8390 available from DOW); and Fluorosurfactants (Fluorad™ FC99C available from 3M). Examples of nonionicsurfactants include: Fluoro surfactants (Fluorad™ FC170C available from3M); Alkoxylate surfactants (Tergitol™ series 15S-5, 15S-7, and 15S-9available from Union Carbide); and Organosilicone surfactants (Silwet™L-77 and L-76-9 available from WITCO).

One or more buffers may optionally be included in the liquid medium tomodulate pH of the ink. The buffers can be organic-based biologicalbuffers or inorganic buffers, preferably, organic-based. Examples ofpreferably-employed buffers include tris(hydroxymethyl)aminomethane(TRIS), available from companies such as Aldrich Chemical (Milwaukee,Wis.), 4-morpholineethanesulfonic acid (MES),4-morpholinepropanesulfonic acid (MOPS), andbeta-hydroxy-4-morpholinepropanesulfonic acid (MOPSO). Further, thebuffers employed should provide a pH ranging from about 3 to about 9 inthe practice of the invention, preferably about 4 to about 6 and mostpreferably from about 4 to about 5.

One or more of the biocides commonly employed in inkjet inks mayoptionally be included in the liquid medium, such as Nuosept™ 95,available from Huls America (Piscataway, N.J.); Proxel™ GXL, availablefrom Zeneca (Wilmington, Del.); and glutaraldehyde, available from UnionCarbide Company (Bound Brook, N.J.) under the trade designation Ucarcide250.

The liquid medium may optionally also include one or more metalchelator. Such chelators are used to bind transition metal cations thatmay be present in the ink. Examples of preferred metal chelatorsinclude: ethylenediaminetetraacetic acid (“EDTA”),diethylenediaminepentaacetic acid (“DPTA”),trans-1,2-diaminocyclohexanetetraacetic acid (“CDTA”),ethylenedinitrilotetraacetic acid (“EGTA”), or other chelators.

In one embodiment inks according to the invention have a pH of fromabout 3 to about 5, preferably from about 3.5 to about 4.5. In anotherembodiment the pH of the ink is preferably from 4 to 11, more preferablyfrom 7 to 10.

The viscosity of the ink at 25° C. is preferably less than 50 cP, morepreferably less than 20 cP and especially less than 5 cP.

The ink may also contain additional components conventionally used inink jet printing inks, for example viscosity and surface tensionmodifiers, corrosion inhibitors and kogation reducing additives.

For the avoidance of doubt, the present invention relates solely to inkscontaining the compound of Formula (1). The scope of protection soughtin this patent specification does not include the compound of Formula(1) per se.

The inks of the present invention provide prints of attractive, neutralblack shades that are particularly well suited for the ink jet printingof text and images. The inks have good storage stability and lowtendency to block the very fine nozzles used in ink jet printers.Furthermore, the resultant images have good optical density,light-fastness, wet-fastness and resistance to fading in the presence ofoxidising air pollutants (e.g. ozone). The inks maybe incorporated intoink jet cartridges and used in ink jet printers by any of the numerousknown methods, for example as described in the many patent applicationsby Hewlett Packard, Seiko Epson, Canon and Lexmark. For example, theinks may be injected into an empty ink jet cartridge and the cartridgere-used in an ink jet printer in the conventional manner.

The invention is further illustrated by the following Example in whichall parts and percentages are by weight unless specified otherwise. Theabbreviation “Ac” means CH₃CO—.

EXAMPLE 1

Preparation of an Ink Comprising:

Preparation of Intermediate 2,5-di-(2-acetoxyethoxy)aniline

Step 1—Preparation of 1,4-bis-(2-acetoxyethoxy)hydroquinone

Hydroquinonebis-(2-hydroxyethyl)ether (179 g), acetic acid (100 ml) andacetic anhydride (300 ml) were stirred and heated under refluxovernight. After cooling to room temperature and drowning into water (2l) the product was isolated by filtration, washed with water, dried andrecrystallised from ethanol to give 212 g of product.

Step 2—Preparation of 2-Nitro-1,4-bis-(2-acetoxyethoxy)hydroquinone

The product of step 1 (211.5 g) was dissolved in acetic acid (1800 ml).A mixture of nitric acid (51.9 ml) and acetic acid (200 ml) was thenadded over 20 minutes keeping the temperature below 20° C. Afterstirring at room temperature overnight the solution was drowned intowater (9 l) and the product isolated by filtration, washed with waterand recrystallised from ethanol to give 209 g of product.

Step 3—Preparation of 2,5-di-(2-acetoxyethoxy)aniline

2-Nitro-1,4-bis-(2-acetoxyethoxy)hydroquinone (115 g) was dissolved inethanol at 50° C. and reduced with hydrogen in the presence of palladiumcatalyst (2 g, 5% Pd/C). When uptake of hydrogen ceased the solution wasscreened to remove the catalyst and the filtrates allowed to cool toroom temperature. The crystalline solid was isolated by filtration anddried under vacuum to give 90 g of product.

Stage One—Preparation ofmonoazo-4-(4-Acetylamino-2-sulpho-3-phenylazo)-2,5-di-(2-acetoxyethoxy)aniline

4-Amino-3-sulphoacetanilide (174 g; 0.6 mol) was stirred in water (2.5l) at pH 9 and sodium nitrite (45.54 g; 0.66 mol) added. The solutionwas added to ice/water containing concentrated hydrochloric acid (180ml) with stirring. After stirring for 1.5 h at less than 10° C. theexcess nitrous acid was destroyed by the addition of sulphamic acid.2,5-di-(2-acetoxyethoxy)aniline (178.2 g; 0.6 mol) was dissolved inacetone (1000 ml) and added to the above diazonium salt suspension at0–10° C. followed by the slow addition of pyridine (30 ml). Afterstirring overnight at room temperature the precipitated product wasfiltered-off, washed with water. The damp paste was then stirred inacetone, filtered and dried (50° C.) to give a an orange solid (210 g;64%).

Stage Two—Preparation of Bisazo Intermediate

The monoazo product from Stage one (24.75 g; 0.05 mol) was dissolved inwater (300 ml) with stirring at pH 10 to which sodium nitrite (6.90 g;0.1 mol) and acetone (200 ml) were added. The resulting mixture was thenadded to 0.10 M hydrochloric acid (70 ml) with stirring at roomtemperature. After stirring for 1 h, the excess nitrous add wasdestroyed by the addition of sulphamic acid. The resulting diazoniumsalt was then added to a stirred solution of chromotropic acid (20.00 g;0.05 mol) at less than 10° C. at pH 7–8 maintained by the addition of 2Nlithium hydroxide when necessary. After stirring overnight the productwas precipitated by the addition of 25% (w/v) lithium chloride thenfiltered and washed with 30% lithium chloride solution. The resultingdamp paste was suspended in water (700 ml) and lithium hydroxide hydrate(25.00 g; 0.60 mol) added and the solution heated at 70° C. After 3 hthe solution neutralised to pH 6–7 by the addition of concentratedhydrochloric acid. The product was precipitated by the slow addition of20% lithium chloride, filtered and washed with 25% (w/v) lithiumchloride solution. The damp paste was dissolved in water and thendialysed to low conductivity. The solution was evaporated to dryness(70° C.) to give a black powder (25.5 g; 67%).Stage Three—Preparation of Title DyeThe amino disazo compound from Stage Two (0.015 mol) in water (160 ml)was stirred at pH 9 to which calsolene oil (1 ml) and sodium nitrite(1.20 g; 0.0174 mol) were added. The resulting solution was stirred thenadded to ice/water (100 g) containing concentrated hydrochloric acid (5ml) with stirring at 0–10° C. After stirring for 1 h at 0–10° C. theexcess nitrous acid was destroyed by the addition of sulphamic acid. Theresulting diazonium salt was added to a stirred solution of1-ethyl-1,2-dihydro-6-hydroxy-4-methyl-2-oxo-3-pyridinecarbonamide (3.10g, 0.158 mol) in water (100 ml) at 0–10° C. and then adjusted to pH 7.After stirring overnight the solution was poured into acetone (3 l) withstirring, filtered and washed with acetone. The solid dissolved in waterand dialysed to low conductivity to give after evaporation (80° C.) ablack powder (8.9 g; 61%; ε_(max) 81,232 and a λ_(max) 601 nm).Stage 4—Preparation of InkAn ink may be prepared having the following formulation:

2-Pyrrolidone 5 parts Thiodiglycol 5 parts Surfynol ™ 465 1 part (fromAir Products Inc., USA) Dye 3 parts Water 86 parts

EXAMPLE 2 INK FORMULATIONS

Further inks described in Tables I and II may be prepared wherein theDye described in the first column is the compound from Example 1.Numbers quoted in the second column onwards refer to the number of partsof the relevant ingredient and all parts are by weight. The inks may becharged into an empty ink jet printer cartridge (e.g. a HP 51625A or51641A cartridge) and applied to paper by thermal or piezo ink jetprinting (e.g. using a HP-DeskJet 340, 540, 600, 840C, 930C or 932cthermal ink jet printer).

The following abbreviations are used in Table I and II:

PG=propylene glycol

DEG=diethylene glycol

NMP=N-methylpyrollidone

DMK=dimethylketone

IPA=isopropanol

MEOH=methanol

2P=2-pyrollidone

MIBK=methylisobutyl ketone

P12=propane-1,2-diol

BDL butane=2,3-diol

CET=Tris(2-aminoethyl)amine buffer

PHO=Na₂HPO₄ and

TBT=tertiary butanol

TDG=thiodiglycol

Print Test Examples

The ink described In Example 1 (stage 4) was ink-jet printed onto avariety of papers using a Hewlett Packard DeskJet 560C™. The CIE colourco-ordinates of each print (a, b, L, Chroma C and hue H) were measuredusing a Gretag Spectrolino Spectrodensitometer™ with 0°/45° measuringgeometry with a spectral range of 400–700 nm at 20 nm spectralintervals, using illuminant D50 with a 2° (CIE 1931) observer angle anda density operation of status A. No less than 2 measurements were takendiagonally across a solid colour block on the print with a size greaterthan 10 mm×10 mm. The properties of the resultant prints are shown inTable 1, where the example number of the dye used to prepare the ink isindicated in the left hand column, and ROD is Relative Optical Density.The substrates used in Tables 1, 2 and 3 were as follows:

TABLE 1 Number HP Printing Paper ™ 1 HP Premium Plus MkII ™ 2 EpsonPremium Photo ™ 3 Ilford Instant Dry ™ 4 SUBSTRATE ROD L a b C H 1 1.1035 0 −12 12 268 2 2.12 8 1 −11 11 274 3 2.12 8 3 −14 14 280 4 2.08 9 0−12 12 269Light FastnessTo evaluate light fastness the prints were irradiated in an Atlas Ci5000Weatherometer™ for 100 hours. The results are shown in Table 3. Thedegree of fade is expressed as ΔE where a lower figure indicates higherlight fastness, and ΔE is defined as the overall change in the CIEcolour co-ordinates L, a, b of the print and is expressed by theequation ΔE=(ΔL²+Δa²+Δb²)^(0.5).

TABLE 2 SUBSTRATE ΔE 1 17 2 10 3 4 4 7Ozone FastnessThe ink from Example 1 (stage 4) was printed onto the substrate shownusing a HP560™ ink jet printer. The printed substrate was then assessedfor ozone stability using an ozone test cabinet from Hampden TestEquipment The test was carried out for 24 hours at 40° C. and 50%relative humidity in the presence of 1 part per million of ozone.Fastness of the printed ink to ozone was judged by the difference in theoptical density before and after exposure to ozone using a GretagSpectrolino Spectrodensitometer. Thus, the lower the % OD loss thegreater the ozone fastness. The results are shown in Table 4 where theexample number of the dye used to prepare the ink is indicated in theleft hand column. These clearly demonstrate that inks based oncompositions of this invention display good ozone fastness.

TABLE 3 SUBSTRATE ROD LOSS % 3 17 4 23

TABLE I Dye Na Content Water PG DEG NMP DMK NaOH Stearate IPA MEOH 2PMIBK 2.0 80 5 6 4 5 3.0 90 5 5 0.2 10.0 85 3 3 3 5 1 2.1 91 8 1 3.1 86 50.2 4 5 1.1 81 9 0.5 0.5 9 2.5 60 4 15 3 3 6 10 5 4 5 65 20 10 2.4 75 54 5 6 5 4.1 80 3 5 2 10 0.3 3.2 65 5 4 6 5 4 6 5 5.1 96 4 10.8 90 5 510.0 80 2 6 2 5 1 4 1.8 80 5 15 2.6 84 11 5 3.3 80 2 10 2 6 12.0 90 70.3 3 5.4 69 2 20 2 1 3 3 6.0 91 4 5

TABLE II Dye Content Water PG DEG NMP CET TBT TDG BDL PHO 2P PI2 3.0 8015 0.2 5 9.0 90 5 1.2 5 1.5 85 5 5 0.15 5.0 0.2 2.5 90 6 4 0.12 3.1 82 48 0.3 6 0.9 85 10 5 0.2 8.0 90 5 5 0.3 4.0 70 10 4 1 4 11 2.2 75 4 10 32 6 10.0 91 6 3 9.0 76 9 7 3.0 0.95 5 5.0 78 5 11 6 5.4 86 7 7 2.1 70 55 5 0.1 0.2 0.1 5 0.1 5 2.0 90 10 2 88 10 5 78 5 12 5 8 70 2 8 15 5 1080 8 12 10 80 10

1. An ink comprising a liquid medium and a tris-azo compound of Formula(1) or salt thereof:

wherein the liquid medium comprises water and an organic solvent.
 2. Anink according to claim 1 which comprises: (a) from 0.01 to 30 parts of acompound of Formula (1) or salt thereof; and (b) from 70 to 99.99 partsof a liquid medium comprising water and an organic solvent; wherein allparts are by weight and the number of parts of (a)+(b)=100.
 3. An inkaccording to claim 2 wherein the number of parts of component (a) isfrom 1 to 5 parts and the number of parts of component (b) is from 99 to95 parts.
 4. An ink according to claim 2 or 3 wherein component (a) iscompletely dissolved in component (b).
 5. An ink according to claim 1wherein the liquid medium comprises one or more anionic and/or nonionicsurfactants.
 6. An ink according to claim 1 wherein the liquid mediumcomprises one or more pH buffers.
 7. An ink according to claim 1 whereinthe liquid medium comprises one or more biocides.
 8. An ink according toclaim 1 wherein the liquid medium comprises one or more metal chelators.9. An ink according to claim 1 having a pH of 3 to
 5. 10. An inkaccording to claim 1 having a viscosity at 25° C. of less than 50 cP.11. In the method of ink jet printing, the improvement wherein the inkis an ink according to claim
 1. 12. An ink jet cartridge containing anink according to claim
 1. 13. A substrate ink jet printed with an inkaccording to claim 1.